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Abstract:

An operating system for an electric motor associated with a hydraulic pump
for moving a load and method of operating the same. The operating system
includes a power source that is electrically connected to the electric
motor wherein a capacitor charge and discharge circuit is used in
association with a capacitor in order to store energy within the
capacitor as the operating system is in use.

Claims:

1. A method of operating an electric motor associated with a hydraulic
pump for moving a load comprising:providing a power source electrically
connected to the electric motor;providing a capacitor charge and
discharge circuit electrically connected to the power source;providing a
capacitor electrically connected to the capacitor charge and discharge
circuit for storing energy therein;drawing current from the capacitor at
a varying voltage as the capacitor is discharged with the capacitor
charge and discharge circuit.

2. The method of claim 1 further comprising the step of providing a system
control circuit electrically connected to the power source.

3. The method of claim 2 further comprising the step of providing a motor
control circuit electrically connected to the electric motor.

4. The method of claim 3 wherein the motor control circuit is an inverter.

5. The method of claim 1 wherein the power source is a direct current
power source.

6. The method of claim 1 further comprising the step of introducing
current into the capacitor at a varying voltage as the capacitor is
charged with the capacitor charge and discharge circuit.

Description:

BACKGROUND OF THE INVENTION

[0001]This invention relates to a power handling and storage system for
industrial material handling trucks. More specifically, this invention
relates to an operating system for an electric motor associated with a
hydraulic pump for moving a load.

[0002]Industrial material handling trucks are used in many industrial
facilities to move products and for loading and unloading of
transportation vehicles. Additionally, the industrial material handling
trucks are used for placing and removing products from shelves and for
other purposes that are well known in the art.

[0003]Such trucks of the present art consume energy to steer and propel
themselves about a facility, to lift and load, and for various other
auxiliary purposes. Specifically, electrohydraulic systems are used in
the raising and lowering of payloads in such trucks. A payload at
elevation possesses a certain degree of potential energy that can
theoretically be captured to charge a battery or for other useful
purposes when a payload is lowered.

[0004]Prior inventions have taught electrohydraulic methods of
electrically regenerating energy while lowering a load. Unfortunately,
regenerative load lowering methods of the prior art have failed because
the regenerative energy charged a lead acid storage battery at a more
rapid rate than the battery could effectively store. Each time that a
regenerative load lowering system attempted to charge a storage battery
at such an excessive rate, cumulative damage occurs to the battery and
only a fraction of the charging current is effectively stored.

[0005]Additionally, a battery maintains a relatively constant voltage as
current is introduced into a battery during charging and as current is
drawn from the battery during discharge. Thus, such applications drain or
charge a battery at a rapid rate for a short period of time thus damaging
the conventional batteries and thereby shortening the life time of the
batteries.

[0006]Prior art references have suggested the use of capacitors that can
be used to store energy; however, these references do not provide how to
control the transfer of energy to the capacitors in such a way to provide
efficient storage of the energy. Similarly, how energy is discharged from
these capacitors is also not taught in a way to provide an efficient
method of operation.

[0007]Therefore, a principal object of the present invention is to provide
an operating system for an electric motor that minimizes loss of energy
in the system.

[0008]Yet another object of the present invention is to utilize a circuit
for introducing current to a regenerative energy storage capacitor to
improve efficiency therein.

[0009]These and other objects, features, or advantages of the present
invention will become apparent from the specification and claims.

BRIEF SUMMARY OF THE INVENTION

[0010]An operating system for an electric motor associated with a
hydraulic pump for moving a load. The operating system includes a power
source that is electrically connected to the electric motor and a
capacitor charge and discharge circuit electrically connected to the
power source. A capacitor is electrically connected to the capacitor
charge and discharge circuits such that the capacitor charge and
discharge circuit introduces current in the capacitor at a varying
voltage as the capacitor is being discharged.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]The Figure is a schematic diagram of an operating system for an
electric motor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0012]The figures show a schematic diagram of the operating system 10 of
an industrial material handling truck 12. Though shown used in
association with an industrial material handling truck the system could
be used with any device that uses an electrohydraulic power source.

[0013]The lift system 14 of the truck 12 contains an electrohydraulic
motor having an electric power means 16 such as an electric motor that is
connected to a hydraulic pump 18. Hydraulic pump 18 is in fluid
communication with a fluid reservoir 20 to provide fluid to a hydraulic
valve 22 to a lift cylinder 24 in order to lift a load 26. Though in a
preferred embodiment hydraulic valves 22 are used, in another embodiment
the hydraulic pump may be in direct fluid flow communication with the
lift cylinder 24 without the use of the hydraulic valves 22. Similarly,
in another embodiment a threaded screw apparatus 27 (FIG. 2) could be
used to lift load 26 without falling outside the scope of this
disclosure.

[0014]The operating system 10 has a control system 28 that utilizes a
power source 30 that in one embodiment is a direct current power source.
Additionally, in a preferred embodiment the power source 30 is a battery.
The power source 30 is electrically connected to the other components of
the system via positive DC bus wires 32 and negative DC bus wires 34.

[0015]Other components of the control system 28 include a capacitor charge
and discharge circuit 36 that is electrically connected to the power
source 30 and to a capacitor 38. Specifically, capacitor 38 is able to
store energy therein to effectively regenerate energy through the system.
The control system 28 additionally has a system control circuit 40 and a
motor control circuit 42 that are electrically connected with the other
components of the control system 28. In a preferred embodiment the motor
control circuit 42 is an inverter. Specifically, the motor control
circuit 42 is electrically connected to the electric power means 16 to
control the electrohydraulic system 14.

[0016]In operation when the lift cylinder 24 is actuated to lower a load
26 the capacitor charge and discharge circuit 36 introduces a varying
voltage to the capacitor 38 as the capacitor 38 is charged. Similarly,
current is drawn from the capacitor 38 at a varying voltage as the
capacitor is discharged. Because the capacitor changes voltage
significantly during charge and discharge the varying input from the
capacitor charge and discharge circuit 36 facilitates and creates a more
efficient storage of energy within the capacitor.

[0017]Persons skilled in the art will realize that any suitable type of
capacitor could be used in the present invention including standard
capacitors, electrolytic capacitors, super capacitors, electrochemical
capacitors are all specifically contemplated in the present invention.
The present invention additionally contemplates that a plurality of
capacitors may be used, arranged in series, parallel, or otherwise. While
the example of lifting and lowering a payload is taught as a means of
using the present invention, persons skilled in the are will realize that
the present invention applies in a like manner to any system that
develops regenerative energy whatever the source of the regenerative
energy including the deceleration and subsequent acceleration of any load
or truck, a change in elevation of a load or truck, or any other source
of regenerative energy within an industrial truck.

[0018]Specifically, the energy stored in a capacitor follows a formula of
E=0.5*C*V 2 wherein E is the total energy stored in joules, C is the
capacitance in farads and V is the voltage across the terminals of the
capacitors. As a result of this changing voltage characteristic the
capacitor charge and discharge circuit 36 is adapted of being capable of
introducing current into the capacitor at a varying voltage as the
capacitor is charged and similarly drawing current from the capacitor at
a varying voltage as the capacitor is discharged. As a result the
capacitor is able to store energy more rapidly than a battery and the
capacitor charge and discharge circuit 36 ensures proper functioning to
create maximum storage and efficiency within the control system 28. Thus,
at the very least all of the stated objectives have been met.

[0019]It will be appreciated by those skilled in the art that other
various modifications could be made to the device without departing from
the spirit in scope of this invention. All such modifications and changes
fall within the scope of the claims and are intended to be covered
thereby.

Patent applications by Jeff Herrin, Ankeny, IA US

Patent applications by Michael D. Gandrud, Ames, IA US

Patent applications by SAUER-DANFOSS INC.

Patent applications in class CAPACITOR CHARGING OR DISCHARGING

Patent applications in all subclasses CAPACITOR CHARGING OR DISCHARGING